Underground storage caverns such as the one described in U.S. Pat. No. 3,049,921 are well known in the art. These storage caverns have proved to be an inexpensive alternative to surface storage equipment such as steel tanks. The caverns also require little maintenance and can be much larger than surface storage equipment.
These underground storage caverns are generally formed in impermeable earth formations either by conventional mining methods, or in some cases, by dissolving the materials with aqueous solvents or the like, to create a storage space in the soluble underground formation. Often salt formations or salt domes are used to create these storage spaces. After formation of the cavern a pool of brine or other fluid which is immiscible with desired stored fluid will be introduced into the lower portion of the cavern and the product to be stored will occupies the space in the upper portion of the cavern over the heavier immiscible fluid.
This immiscible fluid is generally used as a displacing fluid. The fluid is pumped into the lower portion of the cavern so that the stored product can be removed from the upper portion.
A problem that arises with storage caverns is that it is sometimes necessary to mix the product fluids in the caverns. The caverns, however, are often too large to utilize conventional mixing techniques. For example, when storing hydrocarbons, it often happens that the fluids stored over a period of time will vary in density, so that the fluids stratify. When this happens, each layer of fluid will have different properties, such as boiling point, viscosity, etc. To use these fluids in shipping a product to a customer or in various processes, such as fractination, it is necessary that the fluids be mixed to provide a uniform fluid. Conventional mixing has not been effective in providing a uniform mixture without a large investment put into large mixers.
The object of this invention is to provide a uniform mixture of fluids in a storage cavern so that the fluids will be easy to process. A second object is to provide an economical mixing system.